The present invention relates to apparatus for sensing pressure in a body of material.
Apparatus for testing the pressure within materials, through use of an expansible chamber device, are well known. In general, a suitable fluid is supplied to the chamber of the expansible device, and the pressure of that fluid is measured, in order to determine the pressure in the material in which the device is placed.
Among the devices heretofore known is that shown in Steele et al. U.S. Pat. No. 3,427,876, which is a device of some five inches in thickness and includes a support plate having a pressure plate joined to it, the plates being disclosed as being, for example, of steel and welded together. One of the plates has a flange at its periphery, which thereby provides, within the flange, a chamber; transducers are carried in the support plate, fluid connected by passages to the chamber. Such construction is, for some purposes, too thick, and also is unduly expensive.
Also known are Menard U.S. Pat. No. 2,957,341, Noel U.S. Pat. No. 3,349,610 and Goodman et al. U.S. Pat. No. 3,446,062, all of which are of cylindrical construction, and therefore of substantial diameter, requiring a relatively large bore hole.
Further, Johnson U.S. Pat. No. 756,644, Holm et al. U.S. Pat. No. 3,792,608 and Johansen U.S. Pat. No. 4,044,608 disclose apparatus which includes a device, such as a screw-operated pump, to force fluid into a chamber in an expansible device, together with a pressure gauge to indicate the pressure of the fluid.
In general, the heretofore known pressure testing apparatus have not been suitable for use in operations where it is desired to obtain quickly and with minimum preparation a determination of the pressure within a material, and in particular do not lend themselves to placement in very thin slots made in material to be tested, as by a saw.